What do you want to do in Tokyo?
Tokyo has lots of attractions, so if you want to cover everything, of course, 9 days won't be enough. There are many seasonal events happening in Tokyo so if you'd like to participate in such event (summer festivals, new years, halloween, Christmas, cherry blossoms, etc) even staying for a year would not be enough!
If you want to experience major sightseeing stuffs, like visiting Senso-ji Temple, Ueno Park, Tsukiji Fish Market, Tokyo Sky Tree, etc, I think 9 days will be more than enough. If you have 9 days, I would like to say you should take side trips for a day or a night to somewhere other than Tokyo. Such as Kamakura, Kawagoe, Nikko, Hakone, Mt. Fuji, etc. You can see a whole different part of Japan by doing that :)